1. Field of Invention
The present invention relates to an electrode structure and a light emitting diode structure having the electrode structure.
2. Description of Related Art
A conventional light emitting diode structure is composed of a sapphire substrate, an epitaxial layer (e.g., N—GaN, light emitting layer, and P—GaN), a reflection layer, a barrier layer, and a conductive pad. The epitaxial layer, the reflection layer, the barrier layer, and the conductive pad are formed on the sapphire substrate. The reflection layer is usually made of aluminum to reflect light under the conductive pad, so as to enhance the light emitting efficiency of the light emitting diode structure. However, after the aluminum reflection layer has been used for a period of time, aluminum corrosion may occur from the conductive pad, which severely limits the life span of the light emitting diode structure.
Moreover, the current density of the conductive pad and the epitaxial layer may be improved to improve the light emitting efficiency of the conventional light emitting diode structure. However, the integrity of the conventional barrier layer between the conductive pad and the reflection layer is poor. After being used for a period of time, the light emitting diode structure will most likely have an increased impedance of the conductive pad. As a result, when the operation voltage is increased to drive the light emitting diode structure, the reliability analysis (RA) of the light emitting diode structure is not sufficient, such that the maximum allowable value of the current density of the conductive pad and the epitaxial layer is limited. For example, the maximum allowable current density may be two times higher than a standard current density. If the current density is over the maximum allowable current density, the light emitting diode structure will be crashed.